Pete Higgin’s hinted that we should cleanup this hack (asking to do the opacity and then getting the value back out) and finally (due to a weird bug in a WebKit nightly that gave me reason to poke) I cleaned it up:

JavaScript is about run-time. Run-time is great and all, but especially when dealing with the browser, and how your Web page has to bootstrap the entire world on every load, Ajax developers have to think about issues that other people don’t. Problems that others can compile away, or know that “that happens once when I start up the puppy on the server” are here for us to stay.

This often seems to mean that we have to deal with writing our applications in ways that aren’t as clean as we may like. We run across problems where for the Nth time someone was bitten as somewhere code did a “for in” that wasn’t guarded with hasOwnProperty and then someone throws up there arms. Never Again. Dojo does a lot of things out of this experience. It is out of real-world pain that choices were made in the toolkit. One of these is how they are very careful not to pollute the global namespace. This is great in that you don’t run into collisions, especially in a world where code is being sucked in from who knows where (e.g. some Ad code is sucking in things). As the author of some JavaScript code, you don’t actually know what else may get into your global area when running, so you need to guard against it.

The problem is that this means that you can lose out. Prototype feels so right to me in many ways as it is less of a “JavaScript library” than a “way in which JavaScript should have evolved”. We have seen some of its goodness get into ES 3.1 (e.g. bind()) but at that rate of progress we will get four more methods in 20 years ;)

I have to take a second to tease here. Did you notice that there are two trim methods in Dojo? dojo.trim and dojo.string.trim. This is a good example of the crazy things that we have to think about. It appears that dojo.trim is lean code, so it gets into base, but dojo.string.trim is more code, but it runs faster. Wow :)

Once you get a lot of code going, you suddenly realise that the word “dojo” appears 50 times per screen of code. It makes me want to create a Bespin plugin that change the shade of that one word. It feels like Java. Unlike Java, you can’t import away some of the pain. You can try to var foo = some.really.big.package; but that gets annoying quickly.

So, to the point of the blog post. When I saw Alex Russell at a nice wine bar in San Francisco last week, I told him how I would die for the ability to have the best of both worlds of Dojo and Prototype:

I want to be able to write code the way that feels right, without the verboseness, but ALSO not run into the scoping issues. I would even take a performance hit for this. What if I could have:

runSomeCodeWithMagic(function(){// in here I am in the lovely land where "some content ".trim() works// and I can just forEach instead of dojo.forEach// but the outside world isn't affected});

Well, Alex listened to me blather on, probably thinking I was a total idiot, and then went on to quickly indulge me by giving me a little of my wish by giving me dojo.runWith:

Note/warning about the runtime cost: If your browser parses things fully in it’s JS engine up front, this function may hurt. A lot. It de-compiles a function using the toString() method, meaning that it does an uneval + eval + string concat + with() call. Each of these operations alone might be painful in a slow engine. Together they could be fatal. On the other hand, if you’re using these functions in, e.g., Chrome/V8, this could turn out to be relatively cheap, particularly as this is run-once kinda thing. The runtime cost involves namespace misses on locals, and that can be significant. I dunno. You’ll have to test to find out.

Note that you won’t easily be able to define globals from here by dropping a “var”. This might be a feature or a bug, depending on how you think about it.

What about getting the magic on the core objects? Again, only within the magically land of that scope do we want String to have the trim method…. and code outside of it shouldn’t see it. Can we swap onto the objects and their prototypes? Alex has some thoughts here too:

I think I can proxy intrinsics at some additional cost. I’d like to make it a protocol, though, so that you might be able to have a list or function that handles your extensions. E.g.:

This would give us a way to un-install them later, but I don’t have a solution for aync code as we do with with(){ … } which actually binds definitions at declaration time.

I might try to proxy intrinsic prototypes somehow, but I need to spend more time thinking about how to get that to work well. I’d like these things not to place big constraints on how you think about or use this system.

Wicked. This also ties into Pete Higgins and some of the very interesting work he is doing in similar but different veins with his dojotype and plugd which munge Dojo into interesting forms.

Since Dojo has pretty much everything that any other library has, you can start thinking about how you can bend it to look and feel like others, take on their APIs when it makes sense, and bend it to your whim.

With research like Alex’s we could see an interesting view when you can create worlds which don’t affect each other, let you have a view that makes sense for your code, but doesn’t affect others.

Even if you poo-poo some of it for the performance aspects, this is why it is incredibly exciting to see the latest JavaScript Vm work. With these guys running, they can optimize a lot of this a way, and things that used to be bottlenecks in the code will cease to be.

Thanks to Alex and Pete for indulging me, and taking the time to listen and produce really interesting solutions!

Updated: Using the Dojo Loader

James Burke has a very cool follow up on how to give a solution to this kind of problem using the Dojo Loader itself:

Roberto Saccon has given the Bespin project a nice gift, by porting the Bespin codebase to Dojo. This was a lot of work and is very much appreciated. The obvious question is going to be “Why did you decide to change from Prototype to Dojo?”

Firstly, Ben and I really like Prototype. I am a Ruby guy, so it feels good to me. I talked about it a bit here, and I will use Prototype in many projects in the future.

The state of Ajax frameworks is quite interesting. On the one hand, many of the top dogs have actively learned from each other which has lead to many of them offering similar functionality. For example, Dojo and Prototype can do a good job with DOM selectors, which jQuery is known for.

Although you can do a good job in any of the top libraries, they still differ in scope, and are optimized for certain use cases, project sizes, and functionality wants.

jQuery offers a phenomenal API for doing stuff with the DOM. It feels right. It is also trivial to extend this world, which has lead to the huge number of plugins to do just that. Because of the clean, simple API, we have seen a huge surge in jQuery usage and interest. I would say that it is optimal for designers and beginner JavaScript folk. This is not to say that it isn’t also great for experts. There is large support from folks like Simon Willison. John Resig did something amazing. If you think functional, this will be your cup of tea even above and beyond.

Prototype goes a little further in that it offers more sugar on top of the language itself. Some find the strapping on of methods on core Objects as obscene. Personally, I love it. It just feels so much nicer for me to say array.last() or array.include(thing), compared to dojo.indexOf(array, item) > -1 for example. In fact, looking at a bunch of code has me feeling a touch nuts with all of the “dojo.” items in it. My brain is starting to ignore them.

That being said, Dojo’s purity gives you a lot. It may be more verbose to dojo.byId than $, but we have no namespace pollution.

The community quickly wanted us to package up Bespin in a way that we could share things. We wanted the same, and have natural components (e.g. the Editor, Thunderhead itself), and some didn’t like the leakage of the Editor component requiring Prototype which in turn meant pollution into the global namespaces. With Dojo we can hide away nicely, and can even run a build to become foo instead of dojo if we wanted.

Since the community really wanted it, and someone stepped up and actually did it, we accepted the change. On our codebase it had some interesting side effects. For example, before hand we had Prototype, Script.aculo.us, and a slew of third party libraries to give us a bit of this, that, and the other. With Dojo, they had everything we were needing and more, so we could hg rm external/ and be done. We are also doing Comet work and the like, and it fits in nicely.

The first change here was to get Bespin working in Dojo, but now we have more work to make sure that:

The codebase feels Dojo-y

Use more of the Dojo features (e.g. dojo.keys for key handling, CSS store, Comet, …)

Clean up and package our stuff nicely (e.g. bespin vs. editor vs. th)

If you are a Dojo fan, or fancy getting into it anyway, please join in! There are a few Prototype things left around, so some of the spirit is there.

A bit of an aside…

A big pain with Ajax and components, is the whole “I really like that jQuery UI component, but I am using Prototype already…. grrr”. Simon Kaegi of IBM has been putting together some thoughts and code around a JavaScript module system that would enable you to say “I want service X which happens to depend on jQuery, and service Y which depends on Prototype.” I am very interested to see where this goes. We sorely need it! The annoying problem on the client is that having multiple libraries is not cheap. On the server though? Not as big a deal potentially.